1. Field of the Invention
The invention relates to a switching device and a nonvolatile memory device.
2. Background Art
In recent years, the demand for compact memory devices having large capacities typified by NAND flash memory has rapidly increased, and much development is being performed with goals of high bit density and increased capacity. Generally, the capacity of semiconductor memory is increased by downscaling the individual memory elements. However, conventional semiconductor memory technology is reaching limits of downscaling from the viewpoint of operation principles and from the viewpoint of manufacturing cost. Accordingly, the realization of a next-generation memory based on a new operation principle is desired to further increase memory device capacity.
For example, electrochemical switches utilizing graphene (for example, refer to “A graphene-based electrochemical switch,” arXiv 0712.2026V1 and “Nonvolatile Switching in Graphene Field-Effect Device,” IEEE Electron Device Letters, Vol. 29, No. 8, pp. 952-954, August 2008) are considered to be candidates for the next-generation memory that may break through the downscaling limits of conventional semiconductor memory due to their large ON/OFF ratios, nonvolatile properties, and the like.
However, because such conventional technologies utilize electrochemical reactions of water molecules mixed in an insulating film as the reactive substance, the control of the type, position, amount, etc., of the reactive substance is insufficient; the reliability and the yields of the devices are problematic; and many challenges remain before practical use will be achieved.